Patent GB-874600-A (GB)
Title: Improvements in or relating to magnetic chucks and similar holding devices
Inventor: WILLIAMSON JOSEPH CRAWFORD
IPC: B23Q3/154
Filed: 1958-03-28
Abstract: 874,600. Magnets. DARWINS Ltd. June 12, 1959 [March 28, 1958], No. 10048/58. Class 35. A magnetic chuck or holding device in which the holding effort is provided at the edges 4A, 4F, 4C, 4D of at least one pair of plate pole-pieces 2A, 2B, Figs. 1 and 3, cooperating with an assembly of permanent magnet material 1A, 1B having surfaces 2 of opposite magnetic polarity disposed sideby-side, has provision for relative movement of the pole pieces 2A, 2B and the magnetic assembly 1A, 1B, between an " ON " position (Fig. 1) in which each pole-piece is in surface contiguity with an area of magnetic material of one polarity only, and an " OFF " position in which each pole-piece is in surface contiguity with substantially equal areas of opposite polarity, when the magnetic circuit is in effect short-circuited between the pole-pieces so that no holding effort is available at the edges; a permeable work-piece is held when completing the circuit across the pole-pieces with the magnetic assembly is in the " ON " position but is released when the assembly is rotated through 90 degrees to the " OFF " position. The holding effort may be increased by alternating assemblies of magnet plates and pole plates with reversal of polarity between the plates of adjacent assemblies as shown in Fig. 6. The holding face may also be widened by mounting two or more magnet plate assemblies for rotation on parallel 10, in axes 20, Fig. which a single holding face 15 is constituted by the edges of the upper pole plates 16A, the lower pole plates 16B resting on a non-magnetic base 17. The magnet plates 21A, 21B are rotatable in unison by a lever-operated cross-shaft and bevel pinion and quadrant, the shafts 20 being geared together. Alternatively, rectilinear sliding of the plate assemblies in a direction parallel to the holding faces may be effected as shown in Figs. 13 and 16 in which the rectangular plates 32A, 32B of alternating polarity across their width are together slidable between separated pairs of pole plates 33A, 33B, each plate assembly being mounted in a non-magnetic frame 36, Fig. 16, which rests on non-magnetic bolts 37, notches in the lower edges of the pole plates engaging with the bolts. A yoke 40, provided at one end of the frames 36, is movable by a crank 41 to slide the groups of plate assemblies between " ON " and " OFF " positions. Further embodiments are described in which semi-circular or segmental permanent magnet plates, set in plastic or other non- magnetic material, are rotatably mounted within rimmed semi-circular or segmental pole plates, the holding face being provided by the protruding edges of the rims. Magnet plates 43A, 43B, Fig. 21, are retained inside the rimmed pole plates 45A, 45B by a cover plate 50 which is secured to and rotated by a stem 52 and knob 53. A non-magnetic ring 55 surrounds the magnet plates 43A, 43B, the rim 44 enabling the device when turned to the " ON " position, to hold itself against a permeable mass, e.g. a surface plate, and to carry a dial gauge or other device by a stem fitted into a tapped hole 56. A second pair of rimmed pole plates may be placed above the plate assembly with the rims arranged concentrically and flush, or several such units may be combined to form a shallow magnetic chuck. Figs. 22 and 24 show a chuck in which two concentric permanent magnet material assemblies are formed as thin-walled cylinders comprising sectors 57, 58, attached to a non-magnetic base plate 59 which is rotatable through half a sector-arc by a pinion 60 meshing with teeth 61. The sectors 57, 58 are of opposite polarity, the direction of magnetization being radial. Each group of sectors has its own sets of outer and inner pole-pieces in the form of sectors 57A, 57B and 58A, 58B respectively all separated from each other. By means of the pinion 60 the magnet plates may be moved to an " ON " position in which they are in register with the pole plates or to an " OFF " position in which each magnet plate overlaps two outer and two inner pole-pieces. Ceramic magnetic material, e.g. BaO6Fe 2 O 3 , is preferably used for the permanent magnet material. The magnet plate assemblies may be moved slightly beyond the fully balanced " OFF " position to effect slight demagnetization of the workpiece.